Spinal fusion is a procedure used to promote the fusion of two or more vertebrae in efforts to stabilize a damaged or deformed spine. Spinal fixation systems are often used during spinal fusion procedures to temporarily eliminate motion and secure a spinal motion segment in place until sufficient bone growth occurs to fuse the vertebrae together. One example of a commonly utilized fixation system is the pedicle screw construct. The pedicle screw construct typically includes some combination of pedicle screws anchored to the vertebrae of the motion segment(s) to be fixed and one or more fixation rods linking the pedicle screws. While spinal fusion procedures and pedicle screw fixation have a high rate of success, one potential complication of spinal fusion is adjacent segment disease. In adjacent segment disease, the fused motion segment can increase biomechanical stress on the unfused motion segments adjacent to the fused segment leading to changes in intradiscal pressure, hypermobility, and facet joint degeneration. Treatment for adjacent segment disease often involves reoperation on the spine to fuse the affected motion segments with the previously fused segments. Because instrumentation is already present (from the previous fusion procedure) in one of the vertebrae of the motion segment to be newly fused, the surgeon must remove the previously placed fixation rod, and sometimes one or more of the original pedicle screws, in order to create a new construct that spans the adjacent level segment to be fused. Removing this hardware requires exposing segments of the spine that might not otherwise have to be exposed to fuse the adjacent segment. The removal of hardware and the additional exposure it necessitates are undesirable in that it increases the technical demands on the surgeon, length of surgery time, potential for blood loss and other complications, and cost.
The implants and methods described herein are directed towards reducing the challenges associated with the treatment of adjacent segment disease.